A rotary fluid machine disclosed in Japanese Patent Application Laid-open No. 2000-320543 is equipped with a vane piston unit in which a vane and a piston are combined; the piston, which is slidably fitted in a cylinder provided radially in a rotor, interconverts the pressure energy of a gas-phase working medium and the rotational energy of the rotor via a power conversion device comprising an annular channel and a roller, and the vane, which is radially and slidably supported in the rotor, interconverts the pressure energy of the gas-phase working medium and the rotational energy of the rotor.
The vane of such a rotary fluid machine is slidably supported in a vane channel formed radially in the rotor, and by supplying a high pressure liquid-phase working medium to sliding surfaces thereof so as to form a hydrostatic bearing, the vane is floatingly supported, thus greatly reducing the sliding resistance. However, if the liquid-phase working medium, which is used for the hydrostatic bearing and is supplied between the vane and the vane channel, flows into a vane chamber defined by the rotor, the casing, and the vanes, a high temperature gas-phase working medium within the vane chamber is cooled by the low temperature liquid-phase working medium for the hydrostatic bearing, thus giving rise to the problem that the rotary fluid machine cannot exhibit its full performance.